The development of new or improved dosage forms and delivery means for physiologically active agents has been and will continue to be the subject of research for both existing and novel drugs. In too many instances a particular drug dosage provides for more drug than is actually required to produce an efficacious and safe therapeutic blood level free from side effects. The reasons for such theoretically excessive doses are many and include, inter alia, the mode of administration, the metabolism of the drug in the gastrointestinal tract, the absolute absorption (bioavailability) of the drugs and the situs of absorption. In another aspect the use of sustained release dosage forms and delivery means has increased to further both patient compliance and convenience.
More recently, investigations respecting transdermal drug delivery systems have increased resulting in a number of commercially available products especially for the administration of nitroglycerine. These latter systems apparently provide the advantages inherent in sustained delivery dosage forms and avoid the problems of a drug's rapid metabolism upon oral administration. At the same time less drug, although equally efficacious therapeutically to a greater amount orally administered, is ingested or absorbed by the patient. Nevertheless, the feasibility, the success and potential of such transdermal systems have heretofore been limited to drugs that are efficacious at lower dose levels and/or have relatively limited water solubility. The explanation for such limitations arise from the formidable barrier provided by the external layer(s) of animal skin and membrane tissues and the limited body areas which are usefully available for application of such transdermal dosage forms.
Various efforts have been pursued to expand the availability of transdermal delivery to more drugs and overcome the barrier presented by animal skin and membrane. Most such efforts, at least those employing transdermal drug delivery devices, have concentrated on increasing the diffusion of the drug from the device into and through the aforementioned barriers. Other efforts have been more specifically targeted at improving the permeability characteristics or percutaneous absorption capacity of the barrier itself. While some of these latter efforts have reportedly shown some success, the agents employed frequently have caused undesirable systemic side effects as well as tissue damage and irritation at the situs of application.
Agents reported to act as penetration enhancers for transdermal drug delivery include dimethylsulfoxide, disclosed in U.S. Pat. No. 3,551,554; combinations of sucrose fatty acid esters with a sulfoxide or phosphoric oxide, disclosed in U.S. Pat. Nos. 3,896,238; 3,952,099 and 4,046,886; and the 1-substituted azacycloalkan-2-ones which are the subject of U.S. Pat. Nos. 3,989,816; 4,316,893 and 4,405,616.